From German patent DE 43 44 063 C1 it is known to use phosphonic acid functionalities in aqueous binder mixtures as groups for increasing the dispersion stability in water. A description is given for this purpose of reacting polyurethane macromonomers containing free phosphonic acid groups with unsaturated monomers in a free-radical addition polymerization and of subsequently further processing the products with further components to give a binder dispersion. In this way, aqueous binder systems are obtained which contain free phosphonic acid groups directly on the backbone of the binder polymer and which hence exhibit anionic stabilization of the aqueous binder dispersion.
Another function of phosphonic acids or their acidic esters in paint chemistry is described in German laid-open specification DE 10 2004 060 966 A1. Such compounds are used therein, alongside other phosphorus acids, organic acid chlorides, and sulfuric or sulfonic acids, as an additive for stabilizing the reaction of isocyanates with hydroxyl-containing polyacrylates. The use of diesters of phosphonic acid or of diphosphonic acid is not described therein.
Another process for producing a coating for the automobile industry that encompasses the use of phosphonic acids or derivatives thereof is disclosed in German laid-open specification DE 196 50 478 A1. Proposed therein as a substitute for the conventional phosphating and/or for the conventional cathodically deposited corrosion control coating is the application of a tie coat of homopolymers or copolymers of double-bond-containing phosphonic acids or functional phosphonic esters to the metal sheet. In that case the polymers of the new corrosion-inhibiting coat presented can be crosslinked inter/intramolecularly, or to the subsequent coat of paint, by means of functional groups which are not adsorbed on the substrate.
A disadvantage of all of the existing two-component coating systems composed of an isocyanate-based curing agent and a basis system is the rapid reaction after the two components have been mixed. This disadvantage is manifested to an increased extent in the case of the industrial coating of vehicles, which requires a certain preliminary time simply on account of the pipeline systems and the industrial operating regime. As a result, with two-component coating systems in particular, the pot life (i.e., duration of proccessability) of the completed coating formulation becomes an important factor. Moreover, the compatibility of the curing components with the binder components of the basis system is of particular significance. With the known systems, the spectrum of compatibility in this context has to date still been restricted, with the consequence that there may often be incompatibilities between the components in question, so that precise matching is necessary. Moreover, the very same two-component systems that are suitable for producing a clearcoat film ought to combine a good profile of properties with regard to environmental influences with hardness, good optical qualities, and effective scratch resistance.
It is therefore an object of the invention to provide a very substantially universal two-component coating material which is distinguished by a good pot life and which at the same time ensures not only a good appearance but also a sufficient hardness. A further object of the invention, furthermore, is to increase the pot life and the compatibility of the generic two-component clearcoat materials through the use of new adjuvants.